U.S. patent number 6,986,428 [Application Number 10/438,090] was granted by the patent office on 2006-01-17 for fluid separation membrane module.
This patent grant is currently assigned to 3M Innovative Properties Company. Invention is credited to Jonathan F. Hester, Robert S. Kody, Philip D. Radovanovic, Stefan R. Reimann, Brian E. Spiewak.
United States Patent |
6,986,428 |
Hester , et al. |
January 17, 2006 |
Fluid separation membrane module
Abstract
The present invention includes a membrane construction for
selectively transferring a constituent to or from a fluid. The
membrane construction includes a multi-layer fluid impermeable
support sheet having a plurality of supports on at least one side
of the support sheet that form a plurality of flow channels. At
least one layer of the multi-layer support sheet is a bonding
layer. A fluid permeable layer extends over the flow channels and
is bonded to the plurality of the supports by the bonding
layer.
Inventors: |
Hester; Jonathan F. (Hudson,
WI), Spiewak; Brian E. (Inver Grove Heights, MN),
Radovanovic; Philip D. (Duesseldorf, DE), Reimann;
Stefan R. (Cologne, DE), Kody; Robert S.
(Minneapolis, MN) |
Assignee: |
3M Innovative Properties
Company (St. Paul, MN)
|
Family
ID: |
33417499 |
Appl.
No.: |
10/438,090 |
Filed: |
May 14, 2003 |
Prior Publication Data
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|
|
|
Document
Identifier |
Publication Date |
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US 20040226886 A1 |
Nov 18, 2004 |
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Current U.S.
Class: |
210/488; 210/316;
210/321.75; 210/486; 55/498; 55/520; 55/497; 210/321.84; 210/321.6;
210/314 |
Current CPC
Class: |
B01D
65/003 (20130101); C02F 3/102 (20130101); B01D
63/08 (20130101); B01D 63/082 (20130101); B01D
61/00 (20130101); B01D 63/081 (20130101); B01D
2313/105 (20130101); Y02W 10/10 (20150501); B01D
2313/143 (20130101) |
Current International
Class: |
B01D
29/07 (20060101) |
Field of
Search: |
;55/497,498,520
;210/498,486,316,314,321.61,488,321.84,321.75 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0 197 024 |
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Oct 1986 |
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EP |
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0 443 642 |
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Aug 1991 |
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EP |
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0 602 560 |
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Jun 1994 |
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EP |
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0 653 240 |
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May 1995 |
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EP |
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1 142 702 |
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Oct 2001 |
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EP |
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WO 98/01219 |
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Jan 1998 |
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WO |
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WO 99/65664 |
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Dec 1999 |
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WO |
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WO 03/037489 |
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May 2003 |
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WO |
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WO 03/051782 |
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Jun 2003 |
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WO |
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Primary Examiner: Walker; W. L.
Assistant Examiner: Menon; K S
Attorney, Agent or Firm: Little; Douglas B.
Claims
What is claimed is:
1. A membrane construction comprising: a) a multi-layer fluid
impermeable support sheet having a plurality of supports on at
least one side of the support sheet, said supports forming a
plurality of flow channels, at least one layer of the multi-layer
sheet being a bonding layer; and b) at least one fluid permeable
microporous or ultraporous membrane covering a plurality of said
flow channels and bonded to a plurality of said supports by means
of the bonding layer, said bonding layer comprising a resin layer
having a lower softening temperature than the part of the fluid
permeable layer that faces away from the bonding layer, such that
the support sheet is bonded to the fluid permeable membrane by heat
without damaging the structure of the fluid permeable layer of the
membrane construction.
2. The membrane construction of claim 1 in which the multi-layer
fluid impermeable support sheet is in the form of a corrugated
sheet, and the extremities of the corrugations form the
supports.
3. The membrane construction of claim 2 wherein the multi-layer
fluid impermeable support sheet has a cross-sectional configuration
selected from saw tooth and sinusoidal configurations.
4. The membrane construction of claim 1 wherein the supports
comprise rails extending from at least one side of the multi-layer
fluid impermeable support sheet.
5. The membrane construction of claim 4 having support rails on
both sides of the multi-layer fluid impermeable support sheet.
6. The membrane construction of claim 5 wherein the support rails
on one side of the multi-layer fluid impermeable support sheet are
in an offset relationship with respect to the support rails on the
other side.
7. The membrane construction of claim 4 wherein the flow channels
are characterized by smaller sub-channels within the channels, said
sub-channels being formed by minor protrusions between the supports
which minor protrusions do not extend as far from the surface of
the multi-layer impermeable support sheet as do the supports.
8. The membrane construction of claim 1 wherein the fluid permeable
membrane is a water impermeable, gas permeable microporous
membrane.
9. The membrane construction of claim 1 wherein the bonding layer
of the multi-layer fluid impermeable support sheet is made of a
polymeric material selected from the group consisting of polyolefin
elastomers, ethylene vinyl acetate copolymers, ethylene vinyl
acetate terpolymers, styrene-ethylene/butylene-styrene block
copolymers, polyurethanes, polybutylene, polybutylene copolymers,
polyisoprene, polyisoprene copolymers, acrylate, silicones, natural
rubber, polyisobutylene, butyl rubber, and mixtures thereof.
10. The membrane construction of claim 1 wherein the bond between
at least one fluid permeable membrane and the supports is
substantially continuous.
11. The membrane construction of claim 1 further comprising a
manifold connected to the flow channels.
12. The membrane construction of claim 1 wherein the hydraulic
radius of the flow channels is not constant along the length of the
channels.
13. The membrane construction of claim 1 wherein the flow channels
define a tortuous path.
14. The membrane construction of claim 1 wherein the fluid
permeable membrane comprises a microporous or ultraporous membrane
and a fibrous layer.
15. The membrane construction of claim 1 wherein the multi-layer
fluid impermeable support sheet comprises a layer, not the bonding
layer, which comprises a polypropylene resin, a polyethylene resin,
or any combination thereof.
16. The membrane construction of claim 1 in which the fluid
permeable membrane comprises a porous material having a pore size
of less than about 0.8 micrometers.
17. The membrane construction of claim 1 wherein the fluid
permeable membranes have a surface energy of less than about 20
dynes per centimeter.
18. A method of filtering a liquid mixture comprising causing the
liquid to pass through the membrane construction of claim 1 by
means of a pressure difference from one side of the membrane to the
other, the lower pressure being in the flow channels which receive
filtrate.
19. A method of transferring gas to a liquid comprising placing the
membrane construction of claim 1 in the liquid and causing the gas
to flow into the flow channels of the membrane, through the fluid
permeable layer and into the liquid.
20. A method of treating water comprising a) placing the membrane
construction of claim 1 in contact with the water; b) establishing
a mass of bacteria growing on the fluid permeable layer; and c)
causing air or oxygen to flow into the flow channels of the
membrane, through the fluid permeable layer and into the liquid.
Description
TECHNICAL FIELD
The present invention generally relates to a membrane construction
for selectively transferring a constituent to or from a fluid. More
specifically, the present invention relates to a membrane
construction useful in membrane bioreactors (MBRs), membrane
aeration bioreactors (MABRs), and other filtration and mass
transfer apparatus.
BACKGROUND
In U.S. Pat. No. 3,472,765 use of a membrane separation device in a
biological reactor is described for removing one or more
constituents from a fluid mixture by passing a fluid mixture
through a selectively permeable fluid separation medium that is a
component of the separation device. Fluid membrane devices include
membrane modules that generally fall under three membrane
categories: tubular, hollow fiber, and flat sheet porous membranes.
Techniques described in the art that are suitable for manufacturing
membrane modules are disclosed in U.S. Pat. No. 6,284,137-B1, U.S.
Pat. No. 4,230,463, and U.S. Pat. No. 3,615,024.
Flat sheet porous membranes that are included as part of
plate-and-frame modules along with hollow fiber membrane modules
are membrane types used to process water and wastewater. Porous
hollow fiber membrane modules and methods of making them are
described in European Patent Publication 1,166,859-A2, U.S. Pat.
App. 2002/0011443-A1, U.S. Pat. No. 4,440,641; U.S. Pat. No.
4,886,601; U.S. Pat. No. 6,325,928; U.S. Pat. No. 5,783,083; U.S.
Pat. No. 5,639,373, U.S. Pat. No. 5,248,424, U.S. Pat. No.
5,922,201, and U.S. Pat. No. 5,914,039.
Flat sheet porous membrane modules are described in U.S. Pat. No.
5,651,889, and European Pat. Publication 1,127,849-A1. Flat sheet
porous membrane modules can be assembled in pleated cartridges,
spirally-wound modules, or plate-and-frame configurations.
Plate-and-frame flat sheet membrane modules are typically easier to
clean than other types of membrane modules.
Support layers may be used to keep a space between two flat-sheet
membranes to provide for conveyance of fluid to or from the space
between the membranes via a manifold connected to the flat-sheet
membrane modules. Support layers may be in the form of a permeable
mesh designed to keep the membrane module from collapsing under any
internal vacuum or external pressure. Alternatively, support layers
can be in the form of a paper mesh, a non-woven or a woven-fiber
based material. Some examples of support layers are disclosed in
U.S. Pat. No. 4,701,234, U.S. Pat. Nos. 3,679,059, 4,871,456,
4,264,447, and European Pat. No. 0,602,560-B1.
Plate-and-frame module designs may include a support plate rather
than a support mesh to provide strength and rigidity to membrane
modules. European Pat. No. 0,602,560-B1 discloses a structured
support plate that contains a mesh of grooves cut into the support
plate to enhance fluid transfer. U.S. Pat. No. 5,626,751 describes
a module support plate made of metal. Other support plate designs
are found in U.S. Pat. No. 5,482,625 and PCT Publication WO
99/65595.
Attachment of the support layer to the membrane layer can be
accomplished by an adhesive, such as disclosed in U.S. Pat. No.
5,071,553, European Pat. No. 0,653,240-A1, U.S. Pat. No. 5,772,831,
or by melting the membrane, the support plate or both using thermal
fusion or ultrasonic waves, such as disclosed in European Pat. No.
0,602,560-B1, U.S. Pat. No. 5,482,625, U.S. Pat. No. 5,651,888,
U.S. Pat. No. 4,701,234, U.S. Pat. No. 6,287,467-B1, U.S. Pat. No.
4,264,447, and U.S. Pat. No. 4,302,270.
DISCLOSURE OF INVENTION
The present invention includes a membrane construction for
selectively transferring a constituent to or from a fluid. The
membrane construction includes a multi-layer fluid impermeable
support sheet having a plurality of supports on at least one side
of the support sheet that form a plurality of flow channels. At
least one layer of the multi-layer support sheet is a bonding
layer. A fluid permeable layer extends over the flow channels and
is bonded to the plurality of the supports by the bonding layer.
The present invention further includes methods of using the
membrane construction.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a partial cross-section of a membrane construction in
accordance with the present invention.
FIG. 2 is a partial cross-section of an alternate embodiment of the
inventive membrane construction in the form of a corrugated sheet
that includes fluid permeable layers on both sides of the
corrugated sheet.
FIG. 3 is a partial cross-section of another embodiment of the
inventive membrane construction in the form of a sinusoidal
configuration.
FIG. 4 is a partial cross-section of an alternate embodiment of the
inventive membrane construction in the form of a sinusoidal
configured sheet that includes fluid permeable layers on both sides
of the sheet.
FIGS. 5a c are perspective views of multi-layer support sheets that
illustrate flow channels having tortuous flow paths.
FIG. 6 is a cross-sectional view of an alternate embodiment of the
inventive membrane construction illustrating an extruded support
sheet with rails and a fluid permeable layer on one side of the
support sheet.
FIG. 7 is a cross-sectional view of an alternate embodiment of the
inventive membrane construction illustrating the extruded support
sheet with rails and fluid permeable layers on both sides of the
support sheet.
FIG. 8 is a cross-sectional view of an embodiment of the invention
in which the rails on one side of the support sheet are offset from
the rails on the other side.
DETAILED DESCRIPTION
The present invention includes a membrane construction having a
multi-layer fluid impermeable support sheet with a plurality of
supports on at least one side of the support sheet that form a
plurality of flow channels. At least one fluid permeable layer
covers the flow channels and is bonded to the supports by a bonding
layer.
As used herein, the term "microporous" refers to porous films,
membranes or film layers having an average pore size of 0.05 to 3.0
microns as measured by bubble point pore size ASTM-F-316-80.
As used herein, the term "ultraporous" refers to films, membranes
or film layers having an average pore size of 0.001 to 0.05 microns
as measured by bubble point pore size test ASTM-F-316-80.
As used herein, the term "membrane construction" means having a
membrane on a support such that the membrane permits selective
transport of at least one constituent of a fluid mixture through
the membrane while selectively precluding transport of other
constituents.
As used herein, the term "porous membrane" refers to a membrane
having a multiplicity of pores or holes which permit selective
transport of at least one constituent of a fluid mixture through
the structure while selectively precluding transport of other
constituent(s).
As used herein, the term "water-impermeable" means being
impermeable to liquid water under conditions of standard
temperature and pressure.
As used herein, the term "corrugated" means having a shape of folds
or parallel and alternating ridges and grooves.
As used herein, the term "extremities of the corrugations" refers
to the tips of a saw-tooth or curve of a sinusoidal corrugated
profile of a support layer.
As used herein, the term "undulated" means having a wavelike form
or appearance.
As used herein, the term "softening temperature" refers to the
temperature at or above which a polymer component alone or in a
blend with a diluent component will soften.
As used herein, the term "moisture vapor permeable" is used to
describe microporous membrane materials which readily permit the
passage of water vapor through the membrane material but which do
not readily allow the passage of liquid water.
As used herein, the term "hydrophilic" means having a strong
tendency to bind to or absorb water.
As used herein, the term "hydrophobic" is used to describe
microporous membrane materials which are not wet by liquid water,
polar or aqueous solvents, and which are capable of repelling and
preventing the passage of liquid water through the membrane.
As used herein, the term "oleophobic" is used to describe
microporous membrane materials that are not wet by low surface
energy fluids like oils, greases or hydrocarbon solvents. The term
"oleophobic" is also meant to include repelling or tending to not
combine with oil or grease.
A membrane construction 10 in accordance with the present invention
is generally depicted in FIG. 1. The membrane construction 10
includes a fluid permeable layer 12 bonded by a bonding layer 14 to
a multi-layer fluid impermeable support sheet 13 in the form of a
corrugated sheet. The corrugated sheet includes a plurality of
substantially parallel folds 15. The folds are defined by
alternating ridges 16 and grooves 17 with each ridge 16 and groove
17 being defined by conjoining wall sections 18, 19 that are
disposed at angles (which may be acute) with respect to each
other.
The permeable layer 12 is bonded to ridges 16 by bonding layer 14.
Bonding layer 14 may extend along an entire surface of the support
sheet 13 or may be positioned at ridge 16. Bonding layer 14 bonds
tips 20 of ridges 16 to the permeable layer 12 and forms a
substantially continuous seal along the length of tips 20.
The substantially continuous seals along two adjacent ridges with
two adjacent wall sections and the permeable layer 12 form a flow
channel 21 that is discrete and separate from adjacent flow
channels 21. The bonding of the permeable layer 12 along
substantially all of the ridges 16 in a substantially continuous
sealing relationship localizes to that particular flow channel 21
any rupture that may occur to the permeable layer 12 thereby
preventing flooding of the entire membrane construction 10.
An alternative membrane construction 22 includes first and second
permeable layers 23a and 23b bonded to both sides of a multi-layer
fluid impermeable support sheet 24. The permeable layer support
sheet 24 is similar to the support sheet 13 in that is it is in the
form of a corrugated sheet, but the support sheet 24 has bonding
layers 25a and 25b on both sides of the sheet 24. The sheet 24 also
has ridges 26a which are positioned proximate (adjacent to) the
permeable layer 23a and ridges 26b which are positioned proximate
(adjacent to) the permeable layer 23b. The support sheet 24 also
includes grooves 27a positioned proximate the permeable layer 23a
while grooves 27b are positioned proximate the permeable layer 23b.
Conjoining wall sections 28 and 29 which are disposed at angles
(which may be acute) with respect to each other define the ridges
26a and 26b and grooves 27a and 27b.
Similar to the construction described with respect to FIG. 1, the
permeable layers 23a and 23b are bonded to tips 30a of the ridges
26a and to tips 30b of the ridges 26b, respectively. The bonding is
accomplished through bonding layers 25a and 25b. The bonding layers
25a and 25b may extend along the entire surface of the impermeable
support sheet 24 or may be disposed at the tips 30a and 30b of the
ridges 26a and 26b, respectively.
The bond between the tips 30a and 30b and the permeable layer 23a
and 23b, respectively, extends substantially continuously along the
length of each respective ridge. The substantially continuous seal
along two adjacent ridges, whether it is ridges 26a or ridges 26b,
along with two adjacent wall sections, 28, 29, form flow channels
31a and 31b, respectively. Each flow channel is discrete from
adjacent flow channels. The substantially continuous sealing
relationship along the ridges 26a and 26b localizes ruptures to the
particular flow channel that may occur to the permeable layers 23a
and 23b thereby preventing flooding of the entire membrane
construction 22.
Similarly, another membrane construction generally indicated at 32
in FIG. 3 includes a fluid permeable layer 33 bonded by a bonding
layer 34 to a support sheet 35. The support sheet 35 is in a form
of a sinusoidal curve having ridges 36 and grooves 37. The bonding
layer 34 may extend along the entire surface of the sheet 35 but
may be positioned at ridge 36 to provide a bond between the
permeable layer 33 and the support sheet 35. Located between
adjacent ridges 36 and grooves 37 are wall sections 38 and 39. The
wall sections 38 and 39 along with the permeable layer 33 form
discrete flow channels 40. The bonding of the membrane 42 to the
support sheet 35 is a substantially continuous seal along
substantially the entire length of the ridges 36. This
substantially continuous seal localizes to the particular flow
channel 40 ruptures that may occur to the permeable layer thereby
preventing flooding of the entire membrane construction 32.
Similar to the corrugated construction described with respect to
FIG. 2, a sinusoidal construction of the support sheet 43 has
permeable layers 42a and 42b bonded to the support sheet 43 on
opposite sides thereof along ridges 46a and 46b by bonding layers
44a and 44b as illustrated in FIG. 4. The bonding layers 44a and
44b may extend along both surfaces of the support sheet 43 but may
be placed on the ridges so that the permeable layers 42a and 42b
may be bonded to the support sheet 43. Discrete flow channels 48a
and 48b are defined by wall sections 45, 47 of the sinusoidal
curved support sheet 43 and the permeable layers 42a and 42b in a
manner similar to the construction illustrated in FIG. 2.
Although flow channels 21, 31a, 31b, 40, 42a and 42b have been
described as extending along the entire length of the support
sheets 13, 24, 35, 43, respectively, the flow channels 21, 31a,
31b, 40, 42a and 42b need not extend along the entire length of the
support sheets. Additionally, while the flow channels 21, 31a, 31b,
40, 42a and 42b are described as linear, alternative shapes, sizes
or configurations of the flow channels are permissible as long as
the fluid permeable layers 12, 22, 32, and 42 are bonded along the
ridges to form discrete flow channels. For example, the multi-layer
support sheet can be formed to make a tortuous flow channel such as
illustrated in FIG. 5a in a zig-zag configuration, as illustrated
in FIG. 5b in a curved configuration or as illustrated in FIG. 5c
in a maze configuration.
The fluid permeable layer is generally ultraporous or microporous
with pore sizes that may range from about 0.001 micrometers to
about 3.0 micrometers. Preferably, the pore size of the fluid
permeable layer is less than about 0.8 micrometers. The preferred
pore size prevents microbes in wastewater from permeating and
growing in the fluid permeable layer.
The fluid permeable layer may be hydrophilic or hydrophobic
depending on requirements of separation, such as gas-solid,
gas-liquid, liquid-solid, or liquid-liquid separation requirements.
Some non-exhaustive examples of materials that may be used as part
of the fluid permeable layer 12 include polysulfones, cellulose
polymers, polypropylene, polyethylene, polyvinyl chloride,
polyvinylidene fluoride, polytetrafluoroethylene, or any other
combination thereof.
The fluid permeable layer may be any type of filtration media,
including, without limitation, microporous films, ultraporous
films, reverse osmosis membranes, micro-perforated films, non-woven
webs, woven webs, microporous foams, and the like. Additionally,
when using multiple layers of the fluid permeable layer 12, each
layer may be the same or different depending on the separation
goals. For example, the fluid permeable layer can comprise a porous
membrane and a fibrous or non-woven layer.
In general, any suitable technique and apparatus that is useful for
preparing fluid permeable layers may be used to manufacture the
fluid permeable layer 12. For example, porous membranes and
processes for making porous membranes are generally disclosed in
U.S. Pat. Nos. 6,284,137-B1, 4,230,463 and 3,615,024 which are
incorporated herein by reference. Additionally, the fluid permeable
layer may be prepared using a thermally induced phase transition
(TIPT) or thermally induced phase separation (TIPS) processes,
described in detail in U.S. Pat. No. 4,539,256 (Shipman), U.S. Pat.
No. 4,726,989 (Mrozinski), U.S. Pat. No. 4,867,881 (Kinzer), U.S.
Pat. No. 5,120,594 (Mrozinski), and U.S. Pat. No. 5,238,623
(Mrozinski), which are incorporated herein by reference.
Some examples of materials that may be used to form the bonding
layer of the support sheet include polyolefin elastomers, ethylene
vinyl acetate copolymers, ethylene vinyl acetate terpolymers,
styrene-ethylene/butylene-styrene block copolymers, polyurethanes,
polybutylene, polybutylene copolymers, polyisoprene, polyisoprene
copolymers, acrylate, silicones, natural rubber, polyisobutylene,
butyl rubber, and mixtures thereof. Some non-exhaustive examples of
materials that may be used to form the support sheet 13 include a
polypropylene resin, a polyethylene resin, or any combination
thereof.
In general, any suitable technique and apparatus, such as profile
extrusion, microreplication, cast and cure methods, or any other
techniques suitable for manufacturing fluid delivery layers that
are known in the art may be used to prepare the support sheet of
the present invention. As an example, corrugation of a flat sheet
is a suitable technique for making a support sheet having channels
in accordance with the present invention. U.S. Patent Application
No. 2002/0154406 A1 (Merrill et al.) describes an exemplary method
for corrugating a flat polymer film which would be suitable for
preparing corrugated support sheets of the present invention and is
hereby incorporated by reference. Other methods of corrugation are
possible as well.
When profile extrusion is used to prepare a membrane construction
in accordance with the present invention, a multi-layer support
sheet can be formed, as best depicted in FIG. 6. The membrane
construction 60 includes a fluid permeable layer 62 and a
multi-layer support sheet 63. The multi-layer support sheet 63
includes a base 64 and a plurality of spaced-apart substantially
parallel rails 65 extending from the base 63. A low-melting resin
layer is positioned as a tip 66 at a distal end of the rails 65.
Generally, an economical resin, such as a polyolefin resin is
co-extruded with the low-melting resin to form the multi-layer
support sheet 63.
After co-extrusion, the fluid permeable layer 62 is bonded to the
multi-layer support sheet 63 by placing the multi-layer support
sheet 63 adjacent to a surface 67 of the fluid permeable layer 62
and applying sufficient heat and pressure to partially or fully
melt the low-melting resin to form a thermal bond between the fluid
permeable layer 62 and support sheet 63 while avoiding damage to
the fluid permeable layer 62 due to excessive heat and/or pressure.
Flow channels 68 are defined by adjacent spaced-apart rails and the
bonded permeable layer 62.
The low melting resin that is used to form the multi-layer support
sheet typically has a lower softening temperature than the surface
67 of the fluid permeable layer 62. Any resin that has a lower
softening temperature than the fluid permeable layer 62 is suitable
for use so long as a thermal bond between the fluid permeable layer
62 and support sheet 63 is formed without damage to the fluid
permeable layer 62.
Some examples of resins that may be used to form the support sheet
63 include polystyrene, polycarbonate, nylons, ABS
(acrylonitrotrile-butadiene-styrene), fluoropolymers, or polyolefin
resins such as polypropylene, polyethylene, or any combination
thereof. Some non-exhaustive examples of low-melting resins which
may be used to form tips 66 of multi-layer support sheet 63 include
polyolefin elastomers, such as Engage.RTM. ultra-low density
polyethylene resins that are available from DuPont Dow Elastomers,
LLC of Wilmington, Del., and ethylene vinyl acetate copolymers and
terpolymers like Elvax.RTM. ethylene vinyl acetate copolymer resins
that are also available from Dupont Dow Elastomers, LLC of
Wilmington, Del. Other non-exhaustive examples include heat sealing
resins like styrene-ethylene/butylene-styrene block copolymers,
polyurethanes, polybutylene and their copolymers, polyisoprene and
their copolymers, acrylate adhesives, silicones, and rubber-based
adhesives like natural rubber, polyisoprene, polyisobutylene, butyl
rubber or any combination of any of these.
Alternatively, a membrane construction 70, as illustrated in FIG.
7, includes first and second fluid permeable layers 72a and 72b
bonded to a multi-layer support sheet 73 on opposing sides thereof.
The support sheet 73 has a base layer 74 and spaced-apart rails 75a
and 75b extending outwardly from the base 74 in opposite
directions. Flow channels 77a and 77b are defined by adjacent rails
75a or 75b being bonded to first and second fluid permeable layers
72a and 72b, respectively. The bond between the permeable layers
and the rails runs substantially continuously along the length of
the rails thereby providing discrete flow channels wherein, if a
membrane is punctured along one discrete flow channel, the puncture
is localized to that particular flow channel. The membrane
construction 70 is advantageous when treating large volumes of
water or wastewater because it has an increased membrane surface
area.
The multi-layer support sheet 73 of FIG. 7 includes rails 75a and
75b in an aligned configuration and tips 76 made of low melting
polymer (analogous to tips 66 in FIG. 6). Since the support sheet
is produced by extrusion techniques, the rails 75a may be
positioned in an offset relationship from rails 75b as illustrated
in FIG. 8 wherein like reference characters are used to indicate
like elements. Additionally, support sheets having varying rail
heights and sizes may also be prepared using a different die
configuration.
An alternative method which can be used to prepare multi-layer
support sheets having linear flow channels, like those depicted in
FIGS. 6 8, or tortuous flow channels, like those depicted in FIGS.
5a 5c, is microreplication, comprising the steps of (a) providing a
production tool which can be cylindrical and which comprises a
plurality of geometric concavities and corresponding peaks on its
surface corresponding to the features desired in the support sheet;
(b) co-extruding a multi-layer, molten polymer film onto the tool
in excess of the amount required to completely fill the cavities,
thus substantially filling the cavities, the excess forming a layer
of polymer overlying the cavities and the surface around the
cavities; (c) cooling the polymer film, allowing it to solidify and
preserving a permanent surface texture corresponding to that of the
production tool; and (d) continuously stripping from the tool the
solidified polymer (see, for example, WO 99/65664 (Bentsen et al.)
and U.S. Pat. No. 5,077,870 (Melbye et al.), U.S. Pat. No.
5,679,302 (Miller et al.), and U.S. Pat. No. 5,792,411 (Morris et
al.), which are incorporated herein by reference).
When the membrane constructions of the present invention are used
to deliver gas, such as in a membrane aerated bioreactor (MABR),
modification of the membrane surface may be required. Wastewater
typically includes low surface energy fluids such as oil, grease
and surfactant-like molecules that can cause membrane wet-out over
time. Therefore, reducing membrane wet-out by increasing the
resistance of a membrane to absorption of low surface energy fluids
like oil or grease over time is desirable so that membrane
separation efficiency and life is maximized during wastewater
treatment.
One method to increase the resistance of a membrane to absorption
or adsorption of oil or grease over time is to reduce surface
energy of the fluid permeable layer 12. One way to reduce the
surface energy of the fluid permeable layer 12 is to make the fluid
permeable layer 12 oleophobic. Generally, the resistance of a
surface to wetting by low energy fluids increases as the surface
energy of the surface decreases.
Conventional membranes prepared from materials such as
Gore-Tex.RTM. material available from W.L. Gore & Associates,
Inc., typically have surface energies of more than 20 dynes per
centimeter. However, to avoid membrane wet-out by low surface
energy fluids, the inventive membranes may be prepared to have
surface energies of less than about 20 dynes per centimeter.
If the material used to form the fluid permeable layer 12 is not
sufficiently oleophobic or the surface energy is not less than
about 20 dynes per centimeter, the oleophobicity is generally
improved by incorporation of fluorine-containing chemical groups in
a near-surface region of the fluid permeable layer 12.
Incorporation of fluorine-containing chemical groups in the
near-surface region of the fluid permeable layer 12 can be
accomplished by any of the following general techniques: (1)
incorporation of small-molecule or macromolecular fluorinated
additives in the bulk polymer composition used to prepare the fluid
permeable layer; (2) coating the finished fluid permeable layer 12
with a composition comprising fluorinated chemical groups; (3)
exposure of the fluid permeable layer 12 surface to ionizing
radiation or a plasma discharge in the presence of a gaseous
fluorinated species; or (4) providing a fluid permeable layer
polymer and a polymerizable chemical group comprising fluorine, and
initiating the production of reactive groups on either the fluid
permeable layer polymer, the polymerizable chemical group, or both
to effect polymerization and/or graft polymerization of the
polymerizable chemical group on or within the fluid permeable layer
polymer in the vicinity of the surface.
Similarly, when the membrane constructions of the present invention
are used in water filtration, modification of the membrane to make
the membranes more hydrophilic is beneficial. In general,
techniques to make membranes more hydrophilic are known in the
art.
The membrane constructions of the present invention can be used as
part of a membrane module in a fluid filtration system as disclosed
in U.S. Pat. No. 5,639,373, U.S. Pat. No. 5,204,001, U.S. Pat. No.
6,406,629-B1, U.S. Pat. No. 5,192,456, U.S. Pat. No. 6,375,848-B1,
and U.S. Pat. No. 6,303,035-B1 which are incorporated herein by
reference.
The membrane constructions of this invention can be: (1) used in a
wastewater treatment or water treatment facility as part of a
membrane bioreactor such as membrane bioreactors sold by Zenon
Environmental Inc., (Oakville, Ontario, Canada) and Kubota
Corporation (Osaka, Japan) as disclosed in U.S. Pat. No. 6,277,209
and U.S. Pat. No. 5,451,317, which are incorporated herein by
reference, (2) sparged with air bubbles of varying sizes to reduce
biological fouling as disclosed in European Pat. No. 0,510,328-B1,
U.S. Pat. No. 6,193,890-B1, U.S. Pat. App. 2001/0047962-A1, U.S.
Pat. No. 5,192,456, European. Pat. No. 0,700,713-B1, U.S. Pat. No.
5,451,317, European Pat. App. 0,510,328-A2, U.S. Pat. No.
6,224,766, International Pat. App. WO 00/37369, and U.S. Pat. No.
5,944,997, which are incorporated herein by reference, (3) cleaned
using chemicals and/or by back-washing of the membrane
constructions as disclosed in U.S. Pat. App. No. 2001/0052494-A1,
E.P. 1,166,859-A2, European. Pat. No 0,322,753-B1, which are
incorporated herein by reference, and (4) operated with a pressure
gradient across the membrane construction either caused by pressure
from water outside of a submerged membrane module, a hydrostatic
pressure difference, or a vacuum or pressure source connected to a
manifold.
A number of factors affect the performance of a submerged membrane
filter device, such as the way the membrane modules are mounted in
the filtering or bioreactor unit, the spacing of the membrane
modules, the pore size, the membrane materials and the operating
conditions of the actual filtering or bio-reactor unit. These
performance factors are well known in the art and are disclosed in
U.S. Pat. No. 5,192,456, and European Pat. App. 0,937,494-A3 which
are incorporated herein by reference.
The present invention is more particularly described in the
following examples that are intended as illustrations only since
numerous modifications and variations within the scope of the
present invention will be apparent to those skilled in the art.
EXAMPLE 1
A textured fluid impermeable support sheet having rail-like
protrusions on one side was made using conventional profile
extrusion equipment. A polypropylene/polyethylene impact copolymer
(7C06, 1.5 MFI, Dow Chemical Corp., Midland, Mich.) and a
polyolefin elastomer ENGAGE 8100 (Dupont Dow Elastomers,
Wilmington, Del.) were coextruded to form a fluid impermeable
support sheet having a flat base layer with rail-like protrusions
with the upper most surface (tips) of the protrusions containing
the low melting point heat sealable elastomer.
The polypropylene copolymer was extruded with a 6.35 cm single
screw extruder (24:1 L/D) at a rate of approximately 27 kg/hr using
a barrel temperature profile that steadily increased from
177.degree. C. to 232.degree. C. The polyolefin elastomer was fed
at a rate of approximately 2.3 kg/hr into a second single screw
extruder having a diameter of approximately 3.81 cm (28:1 L/D) and
a temperature profile that increased from approximately 204.degree.
C. to 232.degree. C. Both polymers were fed into a MASTERFLEX LD-40
film die (Production Components, Eau Claire, Wis.) maintained at a
temperature of 232.degree. C. The extrudate was extruded vertically
downward through the die equipped with a die lip having a shaping
profile. After being shaped by the die lip, the extrudate was
quenched in a water tank at a speed of approximately 2.1 meter/min
with the water being maintained at approximately 16.degree. C.
20.degree. C. The film die had a die lip having an opening cut by
electron discharge machining configured to form a polymeric base
sheet having a smooth surface on one side and a textured surface
formed of evenly spaced features shaped as rail-like protrusions
extending perpendicularly from the base layer on the opposite side.
The equipment was configured so that the ENGAGE 8100 elastomer was
extruded on the side of the die facing the evenly spaced
features.
The base layer of the support sheet had a thickness of about 102
microns (0.004 in) and was composed of the polypropylene copolymer.
Each rail-like protrusion extended continuously along the base
layer. The dimensions for each rail-like protrusion were
approximately 965 microns (0.038 in) in height, a thickness of
approximately 406 microns (0.016 in), and a center-to-center
spacing of approximately 1016 microns (0.040 in). In addition, each
rail-like protrusion had a layer of approximately 127 microns
(0.005 in) in thickness of the low melting point ENGAGE 8100 at its
distal end (tip). The low melting point resin comprised
approximately 7.7% by weight of the multi-layer support sheet.
EXAMPLE 2
A first fluid impermeable support sheet having protrusions on one
side of the support sheet was extruded using the method of Example
1 and wound into a roll. The first sheet was unwound from a
portable unwind station and fed around rollers such that the smooth
backside passed approximately 1 centimeter beneath the exit of the
die lip. A second fluid impermeable support sheet having
protrusions on one side of the support sheet was extruded using the
method of Example 1 onto the smooth back-side of the first support
sheet such that the resulting dual-layer support sheet had
rail-like protrusions on both sides with a base layer thickness of
about 305 microns (0.012 in), a rail height of about 965 microns
(0.036 in), a rail thickness of about 356 microns (0.014 in), and a
rail center-to-center spacing of about 991 microns (0.039 in). The
dual-sided support sheet had layers of ENGAGE 8100 resin
approximately 127 microns (0.005 in) in thickness on the rail tips
on both sides of the base layer.
EXAMPLE 3
The dual-sided fluid impermeable support sheet of Example 2 was
thermally laminated to a polypropylene thermally-induced phase
separation microporous membrane similar to that described in PCT
Publication WO9929220 Example 1. The membrane had a thickness of
approximately 76 microns (0.003 in), a bubble point pore diameter
of approximately 0.21 microns and an oil content of approximately
35%.
A roll of the dual-sided support sheet was placed on a portable
unwind station with an air brake to provide tension. A roll of the
microporous membrane was placed on a portable unwind station with
an air brake to provide tension to the film.
A series of idler rollers were used to establish a web path such
that the microporous membrane and the support sheet made contact at
a 2 o'clock position on a 30.5 cm (12 in) diameter chrome plated
first nip roll. The nip roll was heated to approximately 74.degree.
C. (165.degree. F.). The low melting point resin-containing tips of
the rails located on the bottom surface of the support sheet made
contact with the microporous membrane with lamination occurring in
about 60 degrees of wrap around the heated nip roll.
A second 30.5 cm (12 in) diameter chrome plated nip roll was
located directly adjacent to the first nip roll. The second roll
was heated to approximately 74.degree. C. (165.degree. F.). Both
rolls were nipped together with a pressure of approximately 276 kPa
(40 psi), using a gap setting of approximately 254 microns (0.010
in) less than the total thickness of the support sheet.
A second roll of the microporous membrane described above was
unwound using a clutch to provide tension and fed into the nip
between the two nip rolls such that the tips of the rails located
on the top surface of the dual-sided support sheet made contact
with the microporous film at approximately the 3 o'clock position
of the first nip roll. The three layer laminate construction
continued to make contact for approximately 90 degrees of wrap
around the second nip roll. A strong bond of the microporous
membranes to the dual-sided support structure resulted.
EXAMPLE 4
A textured fluid impermeable support sheet having rail-like
protrusions on both sides was made using conventional profile
extrusion equipment. A polypropylene/polyethylene impact copolymer
(C104, 1.5 MFI, Dow Chemical Corp., Midland, Mich.) and a
polyolefin elastomer ENGAGE 8100 (Dupont Dow Elastomers,
Wilmington, Del.) were coextruded to form a fluid impermeable
support sheet having a flat base layer with rail-like protrusions
with the upper most surface (tips) of the protrusions containing
the low melting point heat sealable elastomer.
The polypropylene copolymer was extruded with a 6.35 cm single
screw extruder (24:1 L/D) at a rate of approximately 26 kg/hr using
a barrel temperature profile that steadily increased from
216.degree. C. to 246.degree. C. The polyolefin elastomer was fed
at a rate of approximately 1.4 kg/hr into a second single screw
extruder having a diameter of approximately 3.81 cm (28:1 L/D) and
a temperature profile that increased from approximately 204.degree.
C. to 241.degree. C. Both polymers were fed into a 3 layer A-B-A
coextrusion feedblock (Cloeren Co., Orange, Tex.) with the
polypropylene forming the B layer and the elastomer forming the two
A layers. The 3-layer melt stream was fed to an Autoflex 4-H40
extrusion die (Extrusion Dies, Inc., Chippewa Falls, Wis.)
maintained at a temperature of 246.degree. C. The extrudate was
extruded vertically downward through the die equipped with a die
lip having a shaping profile. After being shaped by the die lip,
the extrudate was quenched in a water tank at a speed of
approximately 2.1 meter/min with the water being maintained at
approximately 16.degree. C. 20.degree. C. The film die had a die
lip having an opening cut by electron discharge machining
configured to form a central polymeric base sheet having a
structured surface formed of evenly spaced linear rail-like
protrusions extending perpendicularly from the central base layer
on both sides.
The base layer of the support sheet had a thickness of about 165
microns (0.0065 in). The rail-like protrusions were approximately
838 microns (0.033 in) in height, approximately 262 microns (0.0103
in) in thickness or width, and a center-to-center spacing of
approximately 1346 microns (0.053 in). In addition, each rail-like
protrusion had a layer of approximately 178 microns (0.007 in) in
thickness of the low melting point ENGAGE 8100 at its distal end
(tip). The low melting point resin comprised approximately 4.9% by
weight of the multi-layer support sheet.
EXAMPLE 5
The dual-sided fluid impermeable support sheet of Example 4 was
thermally laminated using the procedure in Example 3 above to a
polypropylene thermally-induced phase separated microporous
membrane similar to that described in PCT Publication WO9929220
Example 1. The microporous membrane comprised approximately 58.75%
by mass polypropylene resin (5D45 Union Carbide Corp. Danbury,
Conn.), 35.0% by mass mineral oil (White Mineral Oil #31 USP Grade
Amoco Oil Company), 4.0% by mass green pigment concentrate
containing 25% by mass green #7 pigment (10066064 FDA Green,
PolyOne Company), and 2.25% by mass fluorocarbon ester (made by 3M
Company and described in U.S. patent application Ser. No.
10/159,752 filed May 29, 2002, page 27 and 28 as citric acid ester
FC 425). In summary, toluene,
C.sub.4F.sub.9SO.sub.2N(CH.sub.3)CH.sub.2CH.sub.2OH (MeFBSE),
citric acid, p-toluene sulfonic acid, and polyethylene alcohol
(obtained as Unilin-425 105-OH equivalent weight from Baker
Petrolite Corp., Sugar Land, Tex.) were mixed together. The mixture
was heated at reflux for 15 hours. When the desired amount of water
was collected in the Dean Stark trap (fitted to the reaction flask)
the toluene was distilled off. When most of the toluene was
distilled off, the molten product was poured into a pan and allowed
to dry in an oven at 120.degree. C. for 4 hours.
The structure of FC-425 is ##STR00001##
The composition for the microporous membrane was melt mixed at 9.08
kg/hr on a 40 mm co-rotating twin screw extruder having a
decreasing barrel temperature profile of 250.degree. C. to
204.degree. C. through a slip gap sheeting die having an orifice
38.1 cm.times.0.381 mm onto a casting wheel maintained at
60.degree. C. The cast film was stretched in a continuous fashion
in the machine direction by a proportion of 1.8:1 at 52.degree. C.
and in the cross direction by a proportion of 1.8:1 at 107.degree.
C. and heat set at 130.degree. C. The resultant microporous
membrane had a surface energy less than 17 dynes/cm.
The membrane had a thickness of approximately 76 microns (0.003
in), a bubble point pore diameter of approximately 0.21 microns and
an oil content of approximately 35%.
EXAMPLE 6
The dual-sided fluid impermeable support sheet of Example 4 was
thermally laminated using the procedure in Example 3 above to a
polypropylene thermally induced phase separated microporous
membrane similar to that described in PCT Publication WO9929220
Examples 7 9. 1.5 percent by weight sorbitan monolaurate (SPAN-20,
Ruger Chemical Co., Inc., Irvington, N.J.) was added to the melt
mixture to render the membrane hydrophilic. The resulting membrane
module element comprised microporous membranes on both sides of the
multi-layer support sheet, the microporous membranes being
hydrophilic and water-permeable.
Although the present invention has been described with reference to
the above embodiments, workers skilled in the art will recognize
that changes may be made in form and detail without departing from
the spirit and scope of the invention.
* * * * *